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Iolite
Iolite Price level: [ what's this? ] Iolite is a semi-precious gemstone that comes in shades of blue, with tones of grey or pale yellow and violet. Iolite is one of those special gemstones that naturally appear different colors depending on their angle in the light. (This is a characteristic of several gemstones and it is called “pleochroism”. Tanzanite is another gemstone that has this same color phenomenon, even in the same hues. For this reason, fine iolite gems often look like fine tanzanites (but at 1/100th of the cost!) Iolite is found in India, Sri Lanka, Mozambique, Tanzania, Zimbabwe and Brazil. It is the gem variety of the mineral cordierite. The rough iolite crystals should be cut in such a way that the deepest violet-blue faces up, so that when we look at the stone from it’s top, the blue-violet color permeates. When iolite gemstones are set in jewelry, the wearer should take care not to knock them about too much. The gems are tolerably hard (meaning they will resist scratches from most materials) but they are brittle, meaning if they are knocked or hit in the right way, fractures may occur inside the stone, or even break a piece off. Read more about the gemological properties of iolite. It is rare to find iolite gems in very large sizes – they are more common in the 3 carat and under range. It is common to see inclusions or fractures inside iolite gemstones. This makes exceptionally clear or “flawless” iolites more valuable because they are rare and beautiful. Read more about how the value of an iolite is determined. The color and pleochrosim of iolite has made it useful to people of ancient times as a tool for understanding the exact angle of the light from the sun. It also gives it special metaphysical properties and symbolism. Read more about the meaning and symbology of iolite. Cordierite (mineralogy) or iolite (gemology) is a magnesium iron aluminium cyclosilicate. Iron is almost always present and a solid solution exists between Mg-rich cordierite and Fe-rich sekaninaite with a series formula: (Mg,Fe)2Al3(Si5AlO18) to (Fe,Mg)2Al3(Si5AlO18).2 A high temperature polymorph exists, indialite, which is isostructural with beryl and has a random distribution of Al in the (Si,Al)6O18 rings.3 Crystal structure of Cordierite Contents hide 1 Name and discovery 2 Occurrence 3 Commercial use 4 Gem variety 5 See also 6 References 7 External links editName and discovery Cordierite, which was discovered in 1813, is named after the French geologist Louis Cordier (1777–1861).2 editOccurrence Cordierite typically occurs in contact or regional metamorphism of argillaceous rocks. It is especially common in hornfels produced by contact metamorphism of pelitic rocks. Two common metamorphic mineral assemblages include sillimanite-cordierite-spinel and cordierite-spinel-plagioclase-orthopyroxene. Other associated minerals include garnet (cordierite-garnet-sillimanite gneisses) and anthophyllite.45 Cordierite also occurs in some granites, pegmatites, and norites in gabbroic magmas. Alteration products include mica, chlorite, and talc. Cordierite occurs in the granite contact zone at Geevor Tin Mine in Cornwall. editCommercial use Catalytic converters are commonly made from ceramics containing a large proportion of cordierite. The manufacturing process deliberately aligns the cordierite crystals to make use of the very low thermal expansion seen for one axis. This prevents thermal shock cracking from taking place when the catalytic converter is used.6 editGem variety As the transparent variety iolite, it is often used as a gemstone. The name "iolite" comes from the Greek word for violet. Another old name is dichroite, a Greek word meaning "two-colored rock", a reference to cordierite's strong pleochroism. It has also been called "water-sapphire" and "Vikings' Compass" because of its usefulness in determining the direction of the sun on overcast days, the Vikings having used it for this purpose7. This works by determining the direction of polarization of the sky overhead. Light scattered by air molecules is polarized, and the direction of the polarization is at right angles to a line to the sun, even when the sun's disk itself is obscured by dense fog or lies just below the horizon.8 Gem quality iolite varies in color from sapphire blue to blue violet to yellowish gray to light blue as the light angle changes. Iolite is sometimes used as an inexpensive substitute for sapphire. It is much softer than sapphires and is abundantly found in Sri Lanka, India, Burma, Australia's Northern Territory, Namibia, Brazil, Tanzania, Madagascar, Connecticut, and the Yellowknife area of the Northwest Territories of Canada. Geologist Dan Hausel, University of Wyoming, found iolite deposits in Wyoming. These are some of the largest deposits in the world. One iolite that he recovered weighed in at more than 24,000 carats--the largest ever found in the world.9